Boron nitride occurs in several polymorphs, among which cubic and hexagonal varieties have been extensively studied over many years and have found numerous practical applications. Although various forms of BN have been used as lubricant and abrasive material for many years, the unique electronic properties of BN have not been yet utilized. Due to their wide optical bandgaps (the widest among nitride semiconductors), cubic and hexagonal polymorphs of BN are promising candidates for optoelectronic devices operating in the deep-ultraviolet range and for high-power electronic devices for switching and radio-frequency applications. The layered structure of hexagonal BN allows preparation of ultrathin nanosheets with very smooth surfaces and low defect density, which are proved to be useful as supporting substrates and gate dielectric layers in graphene-based structures. The first device demonstrations are very encouraging. In this contribution, the recent progress in properties, fabrication technologies, and emerging applications of BN as a wide-gap semiconductor material is reviewed.

Recent Development of Boron Nitride towards Electronic Applications

Cubic boron nitride (c-BN) has been deposited on nitrogen-doped polycrystalline diamond films via plasma-enhanced chemical vapor deposition employing fluorine chemistry. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the c-BN/diamond interface. TEM observations indicated local epitaxy of c-BN on diamond, while h-BN was also observed at the interface. XPS measurements indicated that c-BN growth continued after nucleation. The band offsets between c-BN and diamond were deduced from XPS measurements. The c-BN valence band maximum (VBM) was 0.8 ± 0.1 eV above the diamond VBM, which corresponded to the c-BN conduction band minimum (CBM) of 1.7 ± 0.1 eV above the diamond CBM. Comparison with offsets predicted by theoretical calculations suggests that a C-N interface was obtained.

Band offsets of epitaxial cubic boron nitride deposited on polycrystalline diamond via plasma-enhanced chemical vapor deposition

n-type Si-doped cubic boron nitride (c-BN) (001) layers were heteroepitaxially grown on insulating diamond (001) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The Si donor ionization energy (ED) was estimated to be about 0.24 eV from the temperature dependence of the electron concentration, taking the screening effect into account. Thanks to the low concentration of residual impurities in the MBE-grown c-BN epitaxial layer, the resistivity can be widely varied from about 1 × 108 Ω cm for an undoped c-BN layer to 260 Ω cm for a Si-doped one with a dopant concentration of 1.5 × 1019 cm−3.

Control of n-type electrical conductivity for cubic boron nitride (c-BN) epitaxial layers by Si doping

Boron nitride occurs in several crystalline phases, among which cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) are two of the most interesting wide bandgap materials from both scientific and practical viewpoints. They have been extensively investigated over many years. Due to their wide bandgap, good thermal conductivity, low dielectric constant, and high breakdown field, c-BN and h-BN are promising candidates for optoelectronic devices operating in the deep-ultraviolet range and for high-temperature and high-power electronic devices operating in harsh environments. This chapter first reviews the current status of the synthesis, properties, and characterizations of c-BN thin films, and then analyzes the growth features and proposed mechanisms of c-BN films. Next, some important progress, including stress relief of thick c-BN films and the epitaxial growth of c-BN films, is described. In recent theoretical and experimental research, several dopants, including Be, Mg, Zn, S, C, and Si, have been incorporated into c-BN thin films during deposition or by post ion implantation, resulting in both n- and p-type conduction. The following section of this chapter critically and comprehensively reviews the current status of the doping and electrical properties of c-BN films. Furthermore, the layered structure of h-BN allows the preparation of ultrathin nanosheets with very smooth surfaces and low defect density, which proved to be useful as supporting substrates and gate dielectric layers in two-dimensional (2D) nanoscale electronics. Apart from h-BN thin films, recent progress in properties, synthesis, and emerging applications of 2D h-BN is also reviewed in the last section.

Recent progress of boron nitrides

The recent discovery of direct conversion of hexagonal boron nitride (h-BN) into quenched BN (Q-BN) and single-crystal cubic BN (c-BN) by pulsed laser annealing (PLA) have been implemented to fabri...

Tunable n-Type Conductivity and Transport Properties of Cubic Boron Nitride via Carbon Doping

Phase pure cubic boron nitride (c-BN) films have been epitaxially grown on (001) diamond substrates at 420 °C, 600 °C and 900 °C. Si was added during film growth at these different deposition temperatures in order to achieve in situ n-type doping. The Si concentration increases as the growth temperature decreases. The effects of the different deposition temperatures and the silicon concentration on the transport properties of the c-BN epitaxial films have been systematically investigated. The results demonstrate that the film doped at 420 °C has lower resistivity than the ones doped at elevated temperatures. The temperature dependence of the electron transport properties and their corresponding theoretical fittings reveal that the activation energy of Si doped films is about 0.3 eV and the increased Si concentration could improve the compensation from the deep-level acceptors.

P. Ziemann

Papers

In situ Si doping of heteroepitaxially grown c-BN thin films at different temperatures